Thin, lightweight liquid crystal display apparatuses capable of image display have rapidly become widespread due to price reductions and the development of high-image-quality technology resulting from advances in manufacturing techniques, and are widely used in personal computer monitors, TV receivers, and the like.
A transmissive liquid crystal display apparatus is generally used as a liquid crystal display apparatus. A transmissive liquid crystal display apparatus is equipped with a planar light source called a backlight, illumination light from which is spatially modulated by a liquid crystal panel and forms an image.
A backlight is often used in a scheme where light is incident from a side of a thin guide light plate using a cold cathode fluorescent tube, which is virtually a linear light source. FIG. 1 shows its basic configuration. FIG. 1A is an observed view of a conventional backlight using a cold cathode fluorescent tube from the emitting face side, and FIG. 1B is its sectional view. FIG. 1A omits showing reflector 130 (described later).
As shown in FIG. 1, the light incident from cold cathode fluorescent tube 120 to incident face 111, which is the side of light guide plate 110, propagates repeating total reflections between the opposing main surfaces. A diffuse reflecting layer or projections and indentations for reflections of specific density distribution and size is formed on the surface of reflecting face 113 opposing emitting face side 112, and composed so as to make part of the propagated light emit. By adjusting adequately density and size distribution of the diffuse reflecting layer or the projections and indentations for reflections, it is possible to illuminate uniformly over the whole of the liquid crystal panel.
140 in FIG. 1 shows the reflecting sheet for reflecting light leaking from reflecting face 113 to the emitting face direction to use the light effectively. Further, 150 shows the optical film for controlling directivity of light emitting from the emitting face, and is adequately combined with a diffusion film and a prismatic sheet according to purposes of the light distribution characteristics.
Furthermore, a light emitting diode (hereinafter “LED”) of high luminous efficiency is developed recently and proposed to use for a light source of a backlight of a liquid crystal display.
A method for acquiring planar emission that can be used by lighting back from an LED, which is a point light source, generally includes placing a large number of LEDs at the end face of a light guide plate and inputting light directly. One of the examples is shown in FIG. 2.
FIG. 2 shows configurations of the planar light source in a scheme using LED emitting elements called a side emitter having box-shaped reflecting member in the box-shaped emitting element in the emitting element itself: FIG. 2A is a fragmentally sectional view showing the main part where the light source is the center; and FIG. 2B is a observed view of the light source part from the light guide plate. FIG. 2B omits showing the transparent sealing resin part.
Side emitter LED light source elements 220, which bonds LED chip 221 on element substrate 222 around which reflecting member 223 is provided and sealed by transparent sealing resin 224, and which has connecting terminals 225, are arrayed on wiring substrate 270 and connected.
This light source part is fixed on frame 260 so that the apertures of a plurality of LED light source elements 220 closely face incident face 211 of light guide plate 210.
By constituting as such, it is possible to guide emitting light of which the light source part is stably held in the predetermined place opposing a light guide plate, to the light guide plate. The scheme using LEDs is suitable for use in a thin backlight of a relatively small display size and often used for compact displays such as mobile phones.
However, what happens now is that backlights using LEDs as a light source do not become familiar for large display use such as liquid crystal televisions. One of the causes is that it is difficult to form a compact backlight for large display use requiring large optical output because an LED has limits of density of current feeding through a bonded layer of emitting part and so large chip area is required for acquiring large optical output.
Semiconductor lasers are capable of producing large optical output from small areas compared with LEDs, technology evolution of the basic performance is significantly high including electro-optic conversion efficiency, and so semiconductor lasers become dominant light sources for backlights of large liquid crystal displays in the near future.
Patent Document 1 discloses using a laser light source of wide width emitting light, and reflecting the light by hologram element and guiding the light the side face of the light guide plate.
By this means, a backlight of relatively large area can be expected to be realized by one light source. Patent Document 1: Japanese Patent Application Laid-Open No. 2002-169480